1. Field of the Invention
The present invention relates to an image pickup device, its control method, and a camera.
2. Related Background Art
The specification of U.S. Pat. No. 6,307,195 discloses an image pickup device in which carriers having overflowed from a photodiode while photo carriers are being accumulated overflow into a floating diffusion (FD) region through a transfer gate (TG). In the image pickup device, a part of the carriers having flowed into the floating diffusion region is discarded for expanding the dynamic range of the device. Accordingly, the accumulation time of the floating diffusion region is set to be shorter than the accumulation time of the photodiode. In the configuration described above, it is stated that the dynamic range can be expanded by shortening the accumulation time of the floating diffusion region. However, all of the pieces of information of carriers which have flowed from the photodiode into the floating diffusion region for a period from the start of the accumulation time of the photodiode to the start of the accumulation time of the floating diffusion region are lost. Consequently, an image different from the image which a person actually viewed is picked up.
Moreover, Japanese Patent Application Laid-Open No. 2004-335803 discloses a MOS type image pickup device in which plural light receiving units are arranged on the surface of a semiconductor substrate in the shape of an array and the signal of each light receiving unit is read from each light receiving unit. The image pickup device includes a first signal carrier detection unit which detects incident light to output a signal according to the quantity of the detected incident light. Moreover, the image pickup device includes a second signal carrier detection unit which traps a part of excess carriers of the first signal carrier detection unit when the detection signal of the first signal carrier detection unit has saturated to output a signal according to the quantity of the trapped carriers.
As shown in Japanese Patent Application Laid-Open No. 2004-335803, the second signal carrier detection unit (38), which detects a part of saturated electrons generated in the first signal carrier detection unit (31) when the electrons have saturated, is independently formed. Moreover, the image pickup device has the structure of trapping a part of excess carriers to discard the residual carriers into a vertical overflow drain.
However, in order to discard a part of generated carriers to the vertical overflow drain and to collect the remainder to the second signal carrier detection unit (38), a technique of manufacturing the barrier unit (33) and the vertical overflow drain in a manner of having potential in very high accuracy is necessary. Because dispersion arises in each sample and an inflow rate changes when the accuracy is not adequate, the structure has a drawback of lacking mass productivity remarkably.
Moreover, because the structure is one in which the discharging side of carriers is the vertical overflow drain and the trapping side of carriers is a lateral overflow drain, the carriers are required to go over a barrier between the different structures. Consequently, the structure has a drawback such that the ratio of the carriers flowing out to the vertical overflow drain and the lateral overflow drain has temperature dependence.